Farmer Zhang Xianping rides his pig "Big Precious" during an interview with the media, in Zhangjiakou, Hebei province, China, November 2, 2015. Zhang, a pig breeder, instead of killing it, decided to keep the two-year-old "Big Precious" as pet when its weight reached 600 kg, according to local media. (Photo by Reuters/China Daily)

Freshmen in Zhengzhou Institute of Aeronautical Industry Management head bottles of mineral water for upright stand during military training on September 17, 2015 in Zhengzhou, Henan Province of China. More than 6,800 freshmen in the school are required to take part in the military training. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)

A woman takes a selfie next to a model of Thor during the Middle East Film & Comic Con (MEFCC) in Dubai, United Arab Emirates, Saturday, April 11, 2015. (Photo by Kamran Jebreili/AP Photo)

Revellers continue to party and dance through the night and day during the second day of the San Fermin Running Of The Bulls festival, on July 7, 2014 in Pamplona, Spain. The annual Fiesta de San Fermin, made famous by the 1926 novel of US writer Ernest Hemmingway “The Sun Also Rises”, involves the running of the bulls through the historic heart of Pamplona. (Photo by Christopher Furlong/Getty Images)

A Flemish demonstrator, one of thousands who gathered for a march through Brussels to protest against what the Flemings call their subjucation by the French-speaking Walloons, draws back as he is jeered by a crowd of Walloons on the pavement in a Brussels Street, on October 14, 1962. The Flemish demonstrators clashed with Walloon counter demonstrators as riot police sought to maintain order. The Flemings claim that although they form 60% of the population in Belgium, they are inadequately represented in the government, and they say, the Walloons get most of the top jobs in the armed forces and the diplomatic service. (Photo by AP Photo)

Gas-masked men of the British Machine Gun Corps with a Vickers machine gun during the first battle of the Somme, 1916. (Photo by General Photographic Agency/Getty Images)

A tourist stands on a paddle boat near soldiers taking part on a military and police drill in preparation for the temporary closure of the holiday island Boracay in Philippines on April 24, 2018. (Photo by Erik De Castro/Reuters)

The front wheels of a tractor lift off the ground as the driver moves a heavy trailer outside Peshawar, Pakistan February 19, 2018. (Photo by Fayaz Aziz/Reuters)